The present invention relates to gas turbines having rotational components cooled by a thermal medium flowing in axially extending supply and return tubes within and adjacent the rim of the rotor and particularly relates to retention rings for retaining the bushings about the thermal medium carrying tubes against axial displacement.
In an advanced gas turbine design of the assignee of the present application, a closed cooling circuit is provided for supplying a thermal medium, e.g., cooling steam, generally in an axial direction along the rim of the rotor to turbine buckets to cool the buckets and for returning the spent thermal medium in an opposite, generally axial direction for flow from the rotor, for example, to the steam turbines of a combined cycle system. Generally, in that design, cooling steam is supplied via an axial bore tube assembly, radially outwardly extending tubes and a plurality of axially extending tubes along the rims of the wheels and spacers for supplying steam to the buckets. Spent cooling steam is returned from the buckets through additional axially extending return tubes, radially inwardly extending tubes and the central bore of the bore tube assembly. The axially extending supply and return tubes adjacent the rotor rim are fixed at their aft ends and grow thermally in an axial direction relative to tube-carrying bushings in the wheels and spacers upon turbine startup. Upon turbine shutdown, the tubes thermally contract in an axial direction. There has developed a need for a bushing retention system which will prevent dislodgement of the steam tube bushings as a result of axial thermal growth of the tubes, as well as having the capability to perform their retention function in a very substantial transverse high centrifugal field.
In accordance with a preferred embodiment of the present invention, there is provided a bushing retention system for preventing displacement of the bushings in an axial direction during turbine operation and having the capability of operating in a high centrifugal field. It will be appreciated that each bushing comprises an annular member disposed in a counterbore formed in the openings through the wheel and spacer which receive the steam delivery and return tubes. The inner diameter of the bushing is less than the diameter of the openings through the wheels and spacers and the interior surface of the bushing engages lands formed on the tubes to support the tubes in the openings. An axial face of the bushing engages a shoulder or base of the counterbore, preventing axial movement of the bushing toward that face.
To preclude axial movement of the bushing in the opposite axial direction, the retention system hereof includes a retainer ring for reception in an annular groove of the counterbore at an axial location beyond the adjacent face of the bushing. The retention ring is a split ring, i.e., having a circumferential extent terminating in ends spaced from one another which enables reduction of the outer diameter of the ring to locate the ring in the groove. Once located, the ring projects radially inwardly of the counterbore to afford a stop for the bushing, preventing dislodgement of the bushing in an axial direction. The lands of the tubes support the ring in the high centrifugal field which otherwise tends to drive the ring out of the groove. Particularly, a plurality of circumferentially spaced tabs project radially inwardly from the inner diameter of each ring and preferably have arcuate faces for engaging the tube lands. In this manner, each ring remains sufficiently in the groove, notwithstanding high centrifugal forces, to continue its function of preventing dislodgement of the bushings. Further, the width of the ring in a radial direction decreases in directions circumferentially toward the ends of the ring. This enables the use of a tool inserted into openings at the ends of the rings to readily and easily reduce the diameter of the ring for subsequent expansion and installation in the groove.
In a preferred embodiment according to the present invention, there is provided a bushing retention system in a gas turbine, comprising a gas turbine rotor having a plurality of axially aligned wheels and spacers, a plurality of axially aligned openings through the wheels and spacers with one of the wheels and spacers having counterbores in the openings, a plurality of tubes extending through the openings in the wheels and spacers at circumferentially spaced locations about the rotor for flowing a thermal medium, each counterbore having a radial extending groove thereabout, a bushing in each counterbore of the one wheel and spacer for supporting the tube therein, a retainer ring in each counterbore groove and projecting radially inwardly sufficiently to prevent movement of the bushing in one axial direction, each ring having a circumferential extent terminating in ends spaced from one another enabling reduction of the outer diameter of the ring to locate the ring in the groove, the ring having radial inward tabs for engaging the tube when the ring is subject to substantial centrifugal forces upon rotation of the rotor to maintain the ring within the groove and prevent axial displacement of the bushing in one axial direction.